A comprehensive study is to be carried out on the intracisternal A-particles and extracellular C-type particles associated with BALB/c myeloma cells. The immunochemical, biochemical and physicohemical properties of these particles will be assessed. The biological activity of these particles in terms of their oncogenic activity in vivo and ability to productively infect and/or transform a variety of cells in tissue culture will also be determined. The genetic and biochemical relationship of intracisternal A-particles and C-particles produced by one type of tumor cell will be assessed as will their relationship to the known murine oncornaviruses. Studies will be carried out to determine if the C-type particles associated with BALB/c myeloma are identical or related to the endogenous virus present in BALB/c cells.